Method and apparatus for dynamically controlling read/write operations in a peripheral subsystem

Abstract

A peripheral subsystem includes a peripheral control unit coupled to a plurality of peripheral devices having different read/write speeds. In response to a command from a central processing unit, the peripheral control unit selects one of the devices designated in the command, and polls the device to obtain an indication of the read/write speed of that device. From this speed indication and a density designation included in the command, the peripheral control unit produces a read/write pulse constant which defines the rate at which data is to be read from or applied to the selected peripheral device. Data is then applied to or read from the selected device at the rate defined by the constant.

What is claimed is: 
     
       1. In a data processing system which includes a central processing unit for issuing commands, a peripheral subsystem comprising a plurality of data storage devices, each for operating at a certain speed to record and reproduce data and including means responsive to an interrogation signal for producing a signal indication of the operating speed of the device,   means responsive to a command issued by the central processing unit for applying an interrogation signal to a selected one of said data storage devices,   data register means, and   
     
     
       means responsive to the signal indication produced by the selected device for transferring data between the selected device and the data register means at a rate specified by the signal indication for execution of said commands. 
     
     
       2. Apparatus as in claim 1 wherein each of said data storage devices includes means for recording or reproducing an item of data each time a strobe pulse is applied to the device, and wherein said data transferring means comprises means for storing read/write pulse indices for each data storage device, each of said indices defining the intervals at which strobe pulses are to be applied to the corresponding device for causing the device to record or reproduce data,   means responsive to the receipt of a read/write pulse index for applying strobe pulses to the selected data storage device at intervals defined by the index, and   means responsive to the signal indication produced by the selected device for reading said index from said storing means and applying the index to said strobe pulse applying means.   
     
     
       3. Apparatus as in claim 2 wherein each of said data storage devices further comprises output lines coupled to said data transferring means, means for storing a signal indication of the operating speed of the device, and means responsive to an interrogation signal for causing said signal indication storing means to apply the stored signal indication to the output lines. 
     
     
       4. In a data processing system which includes a central processing unit for issuing commands, a peripheral subsystem comprising a plurality of peripheral devices, each of which operates at some speed to record or reproduce data each time a strobe pulse is received, and each of which includes means responsive to an interrogation signal for producing a speed constant signal specifying the operating speed of the device,   means responsive to a command issued by said central processing unit for applying an interrogation signal to a selected one of the peripheral devices to cause the selected device to produce a speed constant signal,   means for storing density information received in a command from the central processing unit and for storing the speed constant signal produced by the selected peripheral device, said density information specifying the density of data to be applied to or read from the selected peripheral device,   a memory for storing a plurality of data rate indices at different locations in the memory,   means for combining the density information and the speed constant signal to obtain a resultant identifying a location in said memory containing one of said data rate indices,   means for retrieving said one data rate index from the identified location in said memory, and   means for applying strobe pulses to the selected peripheral device at intervals defined by said one data rate index for execution of said commands.   
     
     
       5. Apparatus as in claim 4 wherein said strobe pulse applying means includes means for receiving and storing said one data rate index, a counter, means for applying said one data rate index to said counter to set the counter to a count defined by said one data rate index, clock means for applying pulses to said counter to cause said counter to decrement to a predetermined count, said counter generating a strobe pulse upon decrementing to said predetermined count. 
     
     
       6. Apparatus as in claim 4 further including a first buffer register for temporarily storing data to be applied to and recorded in the selected peripheral device, a second buffer register for temporarily storing data reproduced by the selected peripheral device, and means responsive to a command from said central processing unit for coupling the first and second buffer registers to the selected peripheral device to enable transfer of data from the first buffer register to the selected device and the transfer of data from the selected device to the second buffer register. 
     
     
       7. Apparatus as in claim 6 wherein each of said peripheral devices comprises output lines connected to said coupling means, decoder means for generating an output signal each time an interrogation signal is received from said interrogation signal applying means, and means for storing a speed constant signal specifying the operating speed of the device and for applying the speed constant signal to said output lines each time an output signal is generated by said decoder means. 
     
     
       8. In a data processing system having a central processing unit for issuing commands including a first command which identifies a selected peripheral device and a second command which includes a data density code, a magnetic tape peripheral subsystem comprising a plurality of magnetic tape devices, each of which operates to transport magnetic tape at some speed to record and reproduce data, the data being recorded or reproduced each time a strobe pulse is received by the device, each device including means responsive to an interrogation command for producing a speed constant signal specifying the tape speed of the device,   buffer register means for temporarily storing data and commands to be applied to the magnetic tape devices and for temporarily storing data and signals reproduced by the magnetic tape devices,   means responsive to said first command issued by the central processing unit for coupling said buffer register means with a selected magnetic tape device specified in said first command,   first memory means for storing an interrogation command and a plurality of sets of device constants, each set defining data storage and reproduction timing information for one or more of the magnetic tape devices, each device constant specifying a time interval,   means responsive to the second command issued by the central processing unit for retrieving the interrogation command from said first memory means and applying the interrogation command to the buffer register means for application to the selected magnetic tape device to cause the device to produce a speed constant signal,   second memory means for storing the density code included in said second command and the speed constant signal produced by the selected magnetic tape device,   means for combining the density code and the speed constant signal to produce a resultant identifying a location in said first memory means containing a set of device constants for the selected magnetic tape device,   means for retrieving the set of device constants stored in the identified location, and   means for applying strobe pulses to the selected magnetic tape device with the intervals between the strobe pulses being determined by the device constants of the retrieved set for execution of said commands.   
     
     
       9. In a data processing system comprising a central processing unit for issuing commands, a plurality of peripheral devices, each for recording and reproducing data and for producing a speed constant signal specifying the operating speed of the device, and a peripheral control unit for transferring data between the central processing unit and the peripheral devices in response to the commands from the central processing unit, a method of applying data to and reading data from the peripheral devices at differing rates depending upon the selected device comprising the steps of a. supplying to the peripheral control unit a command coming from the central processing unit which identifies a particular peripheral device,   b. applying an interrogation signal from the peripheral control unit to the particular peripheral device identified in the command,   c. transmitting a speed constant signal to the peripheral control unit from the particular peripheral device, and   d. applying data to or reading data from the particular peripheral device under control of the peripheral control unit and at a rate determined by the speed constant signal supplied by the particular peripheral device for execution of said commands wherein step (d) further comprises   1. recording or reproducing item of data in the particular peripheral device upon receipt of a strobe pulse,   2. producing a read/write pulse index in the peripheral control unit determined by the speed constart signal transmitted from the particular peripheral device, and   3. applying strobe pulses from the peripheral control unit to the particular peripheral device at intervals determined by the read/write pulse index.   
     
     
       10. In a data processing system comprising a central processing unit, a plurality of peripheral devices, and a peripheral control unit interconnecting the central processing unit and the peripheral devices, a method of transferring data between the peripheral control unit and the peripheral devices at differing rates depending upon the selected device comprising the steps of a. transmitting density information from the central processing unit to the peripheral control unit specifying the density of data to be transferred between the peripheral control unit and a selected peripheral device,   b. applying an interrogation signal from the peripheral control unit to the selected peripheral device,   c. transmitting from the selected peripheral device to the peripheral control unit a speed constant signal,   d. storing a plurality of data rate indices at different locations in a memory located within the peripheral control unit,   e. combining the density information and the speed constant signal to obtain a resultant which identifies a location in the memory containing one of the data rate indices, and   f. transferring data between the selected peripheral device and the peripheral control unit for execution of said commands at a rate defined by the data rate index contained in the identified memory location.   
     
     
       11. The method of claim 10 wherein step (f) comprises the steps of  g. setting a counter to a count defined by the data rate index contained in the identified memory location,   h. decrementing said counter to a predetermined count and thereafter applying a strobe pulse to the selected peripheral device,   i. the selected peripheral device, in response to the strobe pulse, recording a data character supplied by the peripheral control unit, and   j. repeating steps (g) through (i) until a predetermined number of data characters have been recorded by the peripheral device.